The present invention relates to systems for driving and controlling cams for internal combustion engines.
One of the conventional systems for driving and controlling cams for internal combustion engines is disclosed, for example, in JP-U 3-77005. This system includes a camshaft rotatably supported on a cylinder head of an internal combustion engine through a bearing to rotate in synchronism with a crankshaft, and a raindrop-shaped cam arranged at the outer periphery of the camshaft to open an intake or exhaust valve against a biasing force of a valve spring. The cam is rotatable relative to the camshaft. A circular groove is formed in an inner peripheral surface of the cam, which is in slide contact with an outer peripheral surface of the camshaft, to be precise, in the inner peripheral surface on the side of a cam lift. On the other hand, a hole is radially formed in the camshaft to correspond to the groove. A pin is arranged in the hole to be capable of moving forward and backward from the outer peripheral surface of the camshaft for engagement and disengagement from the groove. The pin is extruded by the hydraulic pressure within a hydraulic chamber formed in a bottom of the hole. Moreover, the pin is biased in the direction of backward motion by a biasing force of a return spring arranged on the bottom of the hole so as to be received in the hole. Supply and discharge of the hydraulic pressure from the hydraulic chamber are ensured through an oil passage formed axially through the camshaft.
Under low rotation and light load of the engine, supply of the hydraulic pressure to the hydraulic chamber is shut off, so that the pin is received in the hole by a biasing force of the return spring. Thus, the cam is out of coupling with the camshaft to receive no torque therefrom, being retained in the non-rotation state. This brings the valve to be in non-operation, resulting, for example, in improved fuel consumption.
On the other hand, under high rotation and heavy load of the engine, the hydraulic pressure is supplied to the hydraulic chamber through the oil passage, so that the pin is extruded from the hole against a biasing force of the return spring to have an end engaged with the groove at a predetermined rotation timing where the hole correspond to the groove. Thus, the cam is coupled with the camshaft to receive torque therefrom. This actuates the valve in an open and closed way to allow, for example, improved filling efficiency of intake air, resulting in achievement of high power of the engine.
In the above system, however, since the cam and the camshaft are rotatable relative to each other as described above, problems arise such as difficult control for switching from engine low-rotation light-load operation to high-rotation heavy-load operation, i.e. from the released state to the coupled state of the cam and the camshaft, and occurrence of big hammering.
Specifically, during engine low-rotation light-load operation, coupling of the cam with the camshaft is released so that the camshaft is in rotation, but the cam is out of rotation. When passing to engine high-rotation heavy-load operation, the pin of the rotating camshaft protrudes to engage with the groove of the standing cam. Thus, the timing at which the groove corresponds to the hole is difficult to adjust, making smooth engagement of the pin with the groove very difficult. This may result in impossibility of the above switching control.
Moreover, even if the pin can engage with the groove without a hitch, torque of the camshaft acts on an edge of the groove through the pin at the instant when the pin engages with the groove, producing great hammering. This hammering may cause not only damage of the edge of the groove and the end of the pin, but abnormal wear between the groove and the pin.
It is, therefore an object of the present invention to provide a system for driving and controlling a cam for an internal combustion engine, which enables quick and smooth coupling and release of the cam from the camshaft without any occurrence of collision of component parts.
Generally, the present invention provides an internal combustion engine with a valve, comprising:
a camshaft;
a cam which actuates the valve by torque of said camshaft, said cam being movable in a radial direction of said camshaft, said cam including a lift portion which moves forward and backward in a direction of the valve;
a support mechanism which rotates said cam with said camshaft; and
a first device which engages said cam with said camshaft and releases said cam from said camshaft in accordance with engine operating conditions.
One aspect of the present invention is to provide an internal combustion engine with a valve, comprising:
a camshaft;
a cam which actuates the valve by torque of said camshaft, said cam being movable in a radial direction of said camshaft, said cam including a lift portion which moves forward and backward in a direction of the valve;
a support mechanism which rotates said cam with said camshaft; and
means for engaging said cam with said camshaft and releasing said cam from said camshaft in accordance with engine operating conditions.